Univention Corporate Server 4.4 erratum 227 (security)

This update addresses the following issues:
* Backtracking in a regular expression in django.utils.text.Truncator leads
to DoS (CVE-2019-14232)
* The behavior of the underlying HTMLParser leading to DoS (CVE-2019-14233)
* SQL injection possibility in key and index lookups for
JSONField/HStoreField (CVE-2019-14234)
* Potential memory exhaustion in django.utils.encoding.uri_to_iri()
(CVE-2019-14235)